Prior to the present invention, benzopinacol and other tetraarylethanes having the formulas ##STR1## were used as high temperature free radical initiators for the polymerization of vinyl monomers. Additional free radical initiators useful for vinyl monomer polymerization are the corresponding trialkylsilylether derivatives of benzopinacol shown by the formula, ##STR2## disclosed by Rudolph et al, U.S. Pat. Nos. 3,391,355 and Vio, 3,792,126. Oligomeric silyl pinacoles also are shown to be useful as free radical vinyl monomer initiators by Wolfers et al, Offenlegungsschrift No. 2,632,294 and Reuter et al, Offenlegungsschrift No. 3,151,444.
Although the aforedescribed aryl pinacols and silyl derivatives thereof are useful as free radical initiators to effect the polymerization of a variety of free-radical polymerizable organic monomers, such as styrene, methylmethacrylate, etc. these free-radical initiators cannot be used to effect the polymerization of organic monomers in the presence of blocks of polydiorganosiloxane to provide for the production of silicone-organic block polymers.
As taught in my copending application Ser. No. 667,929, polydiorganosiloxanes are provided having terminal or intrachain silylpinacol functional groups, which provide for the production of silicone organic block polymers upon thermolysis of such functionalized silicone polymers in the presence of free-radical polymerizable organic monomers. The polydiorganosiloxane having terminal or intrachain silylpinacole groups can be made by effecting reaction between silicon hydride containing polydiorganosiloxane and aliphatically unsaturated silylpinacol ethers as defined hereinafter.